The present invention relates to a method of separating a plate-like workpiece such as a semiconductor wafer that is held by adhesive on an elastic adhesive pad, from the elastic adhesive pad which has innumerable pores formed in the surface and generates adhesive force when negative pressure is produced by the pores crushed by restoration force generated by elasticity and adhesion.
In the production process of a semiconductor device, a circuit such as an IC or LSI is formed in a large number of areas arranged in a lattice form on the surface of a substantially disk-like semiconductor wafer and each area having the circuit formed therein is diced along predetermined cutting lines to produce a semiconductor chip. To improve the heat radiation property of the semiconductor chip, the thickness of the semiconductor chip is desirably made as small as possible. To enable the downsizing of portable telephones, smart cards, personal computers and the like in which a large number of semiconductor chips are used, the semiconductor chip is desirably formed as thin as possible. To this end, before the semiconductor wafer is divided into chips, the back side of the semiconductor wafer is ground to a predetermined thickness. As a technology capable of further reducing the thickness of the semiconductor chip to be divided, there has also been developed a processing method so-called xe2x80x9cpre-dicingxe2x80x9d which comprises forming dicing grooves having a predetermined depth in the surface of the semiconductor wafer before the grinding of the back side of the semiconductor wafer, and grinding the back side of the semiconductor wafer until the dicing grooves are exposed to divide the semiconductor wafer into semiconductor chips.
The semiconductor wafer or semiconductor chips formed thin as described above are easily broken due to reduced rigidity and hence, considerable care must be taken in handling them in the processing step. The applicant has proposed in Japanese Laid-open Patent Applications 25881/2000 and 158334/2000 (JP-A 2000-25881 and JP-A 2000-158334) a tray comprising an elastic adhesive pad with innumerable pores in the surface for adhesive-holding a plate-like workpiece, making use of negative pressure produced when the pores are crushed by restoration force generated by elasticity and adhesion, in order to enable a thin plate-like workpiece having low rigidity to be carried easily.
When the plate-like workpiece held by adhesion on the tray comprising an elastic adhesive pad is to be separated from the elastic adhesive pad after it has been carried to the predetermined processing step, negative pressure in the pores formed in the surface of the elastic adhesive pad is reduced by supplying air to the elastic adhesive pad, whereby the plate-like workpiece is separated from the elastic adhesive pad. However, in the above method of supplying air to the elastic adhesive pad, it is difficult to supply air to all the pores formed innumerably in the surface of the elastic adhesive pad and considerable suction force may often remain in the elastic adhesive pad. In this case, when the plate-like workpiece is very thin and has low rigidity like a semiconductor wafer or semiconductor chip, it is liable to suffer damage at the time of separation from the elastic adhesive pad.
It is an object of the present invention to provide a method of separating a plate-like workpiece held by adhesion on an elastic adhesive pad, which is capable of separating a plate-like workpiece held by adhesion on an elastic adhesive pad easily.
To attain the above object, according to the present invention, there is provided a method of separating a plate-like workpiece held by adhesion on an elastic adhesive pad from the elastic adhesive pad that has innumerable pores in the surface and generates adhesive force when negative pressure is produced by the pores crushed by restoration force generated by elasticity and adhesion, which comprises the step of separating the plate-like workpiece from the elastic adhesive pad in a state of air in the pores being expanded by heating the elastic adhesive pad at a predetermined temperature.
The above elastic adhesive pad is mounted on a substrate and the substrate is placed on a heating table to heat the elastic adhesive pad via the substrate. Alternatively, the above elastic adhesive pad is mounted on the substrate, and the substrate is provided with a heating element to heat the elastic adhesive pad by heat generated by the heating element. Further alternatively, either one of a hot gas, hot liquid and infrared radiation is supplied to the above elastic adhesive pad to heat the elastic adhesive pad. The heating temperature of the elastic adhesive pad is desirably 40xc2x0 C. to 60xc2x0 C.